使用某些标签WordPress拉出所有帖子

I have this code:

    <div class="col-md-4 col-sm-4 col-xs-12 mob">
  <?php 
  $args = array('tag_slug__and' => array('testtag'));
  $loop = new WP_Query( $args );
  while ($loop->have_posts() ) : $loop->the_post();
  ?>
  <a style="color:#333; text-decoration:none;" href="<?php echo get_permalink(); ?>">
    <?php 
    if(has_post_thumbnail()) {                    
      $image_src = wp_get_attachment_image_src( get_post_thumbnail_id(),'full' );
      echo '<img src="' . $image_src[0]  . '" width="100%"  />';
    } 
    ?>
    <h4><?php the_title(); ?></h4>   

    <?php the_excerpt(); ?>

  <?php endwhile; ?>
  <?php wp_reset_query(); ?>
</a>

Which gets a post which has the tag 'testtag'.

Instead of copying this code, and using 'testtag1', 'testtag2'

How can I just grab ALL the posts which have the tag 'testtag' and just keep adding them into 4 columns?

Any links/help

Nevermind, simple fix!!

 <div class="row" style="margin-top:20px;">

      <?php 
      $args = array('tag_slug__and' => array('testtag'));
      $loop = new WP_Query( $args );
      while ($loop->have_posts() ) : $loop->the_post();
      ?>
      <div class="col-md-4 col-sm-4 col-xs-12 mob">
      <a style="color:#333; text-decoration:none;" href="<?php echo get_permalink(); ?>">
        <?php 
        if(has_post_thumbnail()) {                    
          $image_src = wp_get_attachment_image_src( get_post_thumbnail_id(),'full' );
          echo '<img src="' . $image_src[0]  . '" width="100%"  />';
        } 
        ?>
        <h4><?php the_title(); ?></h4>   

        <?php $trimexcerpt = get_the_excerpt();

        $shortexcerpt = wp_trim_words( $trimexcerpt, $num_words = 10, $more = '… <br/> <a href="">Read More ...</a>' ); 

        echo '<a style="color:#333; text-decoration:none;" href="' . get_permalink() . '"><p>' . $shortexcerpt . '</p></a>'; 

        ?>
  </div>
      <?php endwhile; ?>
      <?php wp_reset_query(); ?>
    </a>

</div>